Position detecting method and apparatus, exposure apparatus and device manufacturing method

ABSTRACT

A position detector suitable for an exposure apparatus includes a reticle stage on which is provided a reticle-stage reference mark constituted by a substrate that exhibits a transmitting property with respect to alignment light. In alignment measurement, the relative position of the reticle-stage reference mark and a wafer alignment mark is detected. The relative position of a reticle reference mark and reticle alignment mark is measured beforehand using a separate detection mechanism, and the relative position of a reticle and wafer is decided from the relative position of the reticle-stage reference mark and wafer alignment mark.

FIELD OF THE INVENTION

[0001] This invention relates to a position detecting method andapparatus in an exposure apparatus for transferring very fine circuitpatterns.

BACKGROUND OF THE INVENTION

[0002] Demagnifying projection exposure using ultraviolet light is usedin lithography for manufacturing extremely fine semiconductor devicessuch as semiconductor memories and logic circuits.

[0003] The smallest dimension of a pattern that can be transferred bydemagnifying projection exposure is proportional to the wavelength oflight used in transfer and inversely proportional to the numericalaperture (NA) of the projection optical system. This means that it isnecessary to shorten the wavelength of the light used to projectextremely fine circuit patterns. For this reason, the wavelength ofultraviolet light used in pattern transfer has become increasinglyshorter, e.g., 365 nm in mercury-vapor lamps, 248 nm in KrF excimerlasers and 193 nm in ArF excimer lasers.

[0004] As semiconductor devices are becoming smaller and smaller at anincreasing rate, there is a limit on what lithography using ultravioletlight can accomplish. Accordingly, in order to burn in an extremely finecircuit pattern of less than 0.1 μm in an efficient manner, ademagnifying projection exposure apparatus using extreme ultravioletlight (EUV light) of shorter wavelength on the order to 10 to 15 nm hasbeen developed.

[0005] Since absorption by the material used is pronounced in the regionof EUV light, a lens-based optical system that utilizes the refractionof light, as in the case of visible or ultraviolet light, isimpractical. An exposure apparatus that employs EUV light, therefore,uses a reflection optical system. In such case use is made of areflecting-type reticle in which the pattern to be transferred is formedon a mirror using an absorbing body.

[0006] A multilayer mirror and an oblique-incidence total-reflectionmirror are examples of reflecting-type optical elements for constructingan exposure apparatus that relies upon EUV light. In the EUV region, thereal part of the index of refraction is much smaller than unity and, asa result, total reflection occurs if use is made of oblique incidence inwhich the EUV light just barely impinges upon the mirror surface.Usually, a high reflectivity of 20 or 30% or more is obtained by obliqueincidence of within several degrees measured from the surface. However,because such oblique incidence diminishes degree of freedom in terms ofoptical design, it is difficult to use an oblique-incidencetotal-reflection mirror in a projection optical system.

[0007] A multilayer mirror obtained by building up alternating layers oftwo types of substances having different optical constants is used as amirror for EUV light employed at an angle of incidence close to that ofdirect incidence. For example, molybdenum and silicon are formed inalternating layers on the surface of a glass substrate polished to havea highly precise surface shape. The layer thicknesses of the molybdenumand silicon are, e.g., 0.2 nm and 0.5 nm, respectively, and the numberof layers is 20 each. The thickness of two layers of the differentsubstances is referred to as the “film cycle”. In the above example, thefilm cycle is 0.2 nm+0.5 nm=0.7 nm.

[0008] When EUV light impinges upon such a multilayer mirror, EUV lightof a specific wavelength is reflected. Only EUV light of a narrowbandwidth centered on a wavelength X that satisfies the relationship ofBragg's equation

2×d×sinθ=λ

[0009] where λ represents the wavelength of the EUV light and d the filmcycle, will be reflected efficiently. The bandwidth in this case is 0.6to 1 nm.

[0010] The reflectivity of the reflected EUV light is 0.7 at most, andthe unreflected EUV light is absorbed in the multilayer films or in thesubstrate. Most of this energy is given off as heat.

[0011] Since a multilayer mirror exhibits more loss of light than amirror for visible light, it is necessary to hold the number of mirrorsto the minimum. In order to realize a broad exposure area using a smallnumber of mirrors, use is made of a method (scanning exposure) in whicha large area is transferred by causing a reticle and a wafer to performscanning using fine arcuate areas (ring fields) spaced apart from theoptical axis at fixed distances.

[0012]FIG. 5 is a schematic view illustrating a demagnifying projectionexposure apparatus that employs EUV light according to an example of theprior art. This apparatus includes an EUV light source, a illuminatingoptical system, a reflecting-type reticle, a projection optical system,a reticle stage, a wafer stage, an alignment optical system and a vacuumsystem.

[0013] By way of example, a laser plasma light source is used as the EUVlight source. In the example shown in FIG. 5, a target material(supplied from a target supply unit 502) placed in a vacuum vessel 501is irradiated with pulsed laser light (laser light that is produced byan excitation pulse laser 503 and supplied via a condensing lens 504), ahigh-temperature plasma is produced and EUV light having a wavelengthof, say, 13 nm that emanates from the plasma is utilized as the EUVlight source. A thin film of metal, an inert gas or a droplet is used asthe target material, which is fed into the vacuum vessel 501 by meanssuch as a gas jet (the target supply unit 502). In order to increase theaverage intensity of the EUV light emitted, the pulsed laser should havea high repetition frequency and the apparatus should be operated at arepetition frequency of several kilohertz.

[0014] The illuminating optical system that introduces the light fromthe EUV light source to a reticle 550 comprises a plurality ofmultilayer mirrors or a plurality of oblique-incidence mirrors and anoptical integrator, etc. A condensing mirror (first mirror 506 of theilluminating system) constituting the first stage functions to collectEUV light emitted from the laser plasma substantially isotropically. Anoptical integrator 507 functions to illuminate the reticle uniformlyusing a prescribed numerical aperture. An aperture (field-angle limitingaperture 510) for limiting to a circular arc the area of the reticlesurface that is illuminated is provided at a conjugate point withrespect to the reticle disposed in the illuminating optical system.

[0015] Reflected light from the optical integrator 507 is reflected by asecond mirror 508 of the illuminating system, passes through thefield-angle limiting aperture 510 and is reflected again by a thirdmirror 509 of the optical system, thereby arriving at the reticle 550.

[0016] The projection optical system uses a plurality of mirrors (firstthrough fourth mirrors 511 to 514). Though using a small number ofmirrors allows EUV light to be utilized very efficiently, this makes itdifficult to correct for aberration. The number of mirrors needed tocorrect for aberration is four to six. The shape of each of thereflecting surfaces of the mirrors is convex or concave spherical, orconvex or concave aspherical. The numerical aperture NA is 0.1 to 0.3.

[0017] To fabricate the mirror, use is made of a substrate consisting ofa material, such as glass having a low coefficient of expansion orsilicon carbide, that exhibits a high rigidity and hardness and a smallcoefficient of expansion, the substrate is formed to have a reflectingsurface of a predetermined shape by grinding and polishing, andmultilayer films such as molybdenum and silicon are formed on thereflecting surface. In a case where the angle of incidence is notconstant owing to the location of the layer in the mirror surface, thewavelength of the EUV light, the reflectivity of which rises dependingupon the location, shifts if use is made of multilayer films having afixed film cycle, as is evident from Bragg's equation cited above.Accordingly, it is required that a film-cycle distribution be providedin such a manner that EUV light of the same wavelength will be reflectedefficiently within the mirror surface.

[0018] A reticle stage 552 and a wafer stage 562 have a mechanism inwhich scanning is performed synchronously at a speed ratio proportionalto the reducing magnification. Let X represent the scanning direction inthe plane of the reticle 550 or wafer 560, Y the direction perpendicularto the X direction, and Z the direction perpendicular to the plane ofthe reticle 550 or wafer 560.

[0019] The reticle 550 is held by a reticle chuck 551 on the reticlestage 552. The reticle stage 552 has a mechanism for high-speed movementin the X direction. Further, the reticle stage 552 has a fine-movementmechanism for fine movement in the X, Y and Z directions and for finerotation about these axes, thus making it possible to position thereticle 550. The position and attitude of the reticle stage 552 aremeasured by laser interferometers (not shown) and are controlled basedupon the results of measurement.

[0020] The positional relationship between the position of the reticle550 and the optical axis of the projection optical system and thepositional relationship between the position of the wafer 560 and theoptical axis of the projection optical system are measured by analignment detection mechanism that includes alignment detecting opticalsystems 553, 563, and the positions and angles to the reticle stage 552and wafer stage 562 are set in such a manner that the projected image ofthe reticle will coincide with a predetermined position on the wafer.

[0021] Further, the focus position along the Z axis on the wafer surfaceis measured by a focus-position detecting mechanism that includes afocus detecting optical system 564, and the position and angle of thewafer stage 562 are controlled. During exposure, therefore, the surfaceof the wafer is always maintained at the position at which the image isformed by the projection optical system.

[0022] When one scanning exposure of the wafer ends, the wafer stage 562is stepped in the X and/or Y directions to move the stage to thestarting position of the next scanning exposure, then the reticle stage552 and wafer stage 562 are again scanned synchronously in the Xdirection at a speed ratio that is proportional to the magnification ofthe projection optical system.

[0023] Thus, an operation for synchronously scanning the reticle andwafer in a state in which the demagnified projection image of thereticle is formed on the wafer is repeated (by a step-and-scanoperation). The transfer pattern of the reticle is thus transferred tothe entire surface of the wafer.

[0024] In the conventional EUV exposure apparatus, the followingproblems arise in a case where consideration is given to TTL(Through-the-Lens) alignment in which the relative positioning (referredto as alignment below) between a reticle and a wafer is carried out viaa reflecting-type reticle and multilayer mirrors using non-exposinglight:

[0025] Since the reflecting-type reticle and multilayer mirrors areoptimized to obtain a high reflectivity with EUV light, sufficientreflectivity is not obtained with regard to alignment light that isnon-exposing light, and it is conceivable that highly precise alignmentwill not be achieved. Accordingly, there is need of an optical system inwhich satisfactory alignment signal light is obtained at all times inorder to achieve alignment.

[0026] Furthermore, the alignment detecting optical system must takeinto consideration space-relation limitations. For example, the exposinglight must not be blocked when alignment detection is not carried out.As a consequence, a limitation is imposed upon the structures of thedetection system and detection optical system.

[0027] In the ordinary projection exposure apparatus, a method ofaligning the reticle and wafer via a projection lens is referred to asTTL alignment. In an EUV exposure apparatus, however, the projectionoptical system is constituted not by lenses but by the multilayer-mirroroptical system. It is difficult to refer to this scheme as a TTL scheme.However, for the sake of simplifying the description, an alignmentsystem that uses the intervention of a multilayer-mirror optical systemwill also be defined as being a TTL alignment scheme in thisspecification.

SUMMARY OF THE INVENTION

[0028] Accordingly, an object of the present invention is to prevent adecline in the amount of light of an alignment signal and to make itpossible to construct a highly precise alignment detecting opticalsystem.

[0029] Another object of the present invention is to mitigatelimitations relating to the structure of the detecting system anddetection optical system.

[0030] According to the one aspect of the present invention, a method ofdetecting relative position of a reflecting-type reticle and substrate,the reticle having an alignment mark thereon is provided. The methodcomprises: a holding step of holding the reticle on a reticle stagewhich has a reference mark; and a first detection step of detectingrelative position of the reference mark of the reticle stage, and thealignment mark on the reticle.

[0031] Other features and advantages of the present invention will beapparent from the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings, which are incorporated in andconstitute a part of the specification, illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

[0033]FIG. 1 is a schematic view illustrating a semiconductor exposureapparatus that includes a position detecting apparatus according to afirst embodiment of the present invention;

[0034]FIG. 2 is a schematic view illustrating a semiconductor exposureapparatus that includes a position detecting apparatus according to thefirst embodiment;

[0035]FIG. 3 is a schematic view illustrating a semiconductor exposureapparatus that includes a position detecting apparatus according to asecond embodiment of the present invention;

[0036]FIG. 4 is a schematic view illustrating a semiconductor exposureapparatus that includes a position detecting apparatus according to thesecond embodiment;

[0037]FIG. 5 is a schematic view illustrating a demagnifying projectionexposure apparatus using EUV light;

[0038]FIG. 6 is a diagram useful in describing the flow of a devicemanufacturing process;

[0039]FIG. 7 is a diagram useful in describing a wafer process;

[0040]FIG. 8 is a diagram useful in describing detection of contrast andS/N ratio of a video signal (alignment signal);

[0041]FIG. 9 is a diagram illustrating the path of alignment light in areflecting optical system;

[0042]FIG. 10 is a flowchart useful in describing a procedure formeasuring alignment according to the first embodiment;

[0043]FIG. 11 is a flowchart useful in describing a procedure formeasuring alignment according to the second embodiment; and

[0044]FIG. 12 is a flowchart useful in describing a procedure forselecting alignment procedures according to the first and secondembodiments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] Preferred embodiments of the present invention will now bedescribed in detail in accordance with the accompanying drawings.

[0046] In the description that follows, it is assumed that the exposureapparatus is an EUV exposure apparatus that employs a projection opticalsystem using a multilayer reflecting mirror. However, the presentinvention is not limited to this arrangement. For example, the inventionis applicable to an exposure apparatus that employs a projection opticalsystem using lens, and to a proximity exposure apparatus (typified by anX-ray exposure apparatus).

[0047] [First Embodiment]

[0048]FIGS. 1 and 2 are schematic views illustrating a semiconductorexposure apparatus that includes a position detecting apparatusaccording to a first embodiment of the invention. The alignmentmechanism of the semiconductor exposure apparatus according to the firstembodiment, as well as the operation of this mechanism, will bedescribed with reference to FIGS. 1 and 2.

[0049] As shown in FIG. 1, an illuminating optical system 2 comprises alight source, which emits non-exposing light, and illuminating optics.The illuminating light from the illuminating optical system 2 isreflected by a half-mirror 13 and mirror 14 so as to illuminate atransmitting-type alignment mark (referred to as a reticle-stagereference mark) 3 disposed on a reticle stage 4 through a transparentportion or an aperture of the reticle stage 4. It should be noted that aportion of the reticle-stage reference mark 3 is transmissive withrespect to the wavelength of the non-exposing light from theilluminating optical system 2. Preferably, the reticle-stage referencemark 3 is constituted by a substrate having optimum transmittance withrespect to the alignment light and an opaque pattern thereon.

[0050] The illuminating light that has passed through the reticle-stagereference mark 3 passes through a multilayer-mirror optical system 7 andilluminates a wafer alignment mark 9 on a wafer 10. FIG. 9 illustratesthe path of the alignment light.

[0051] The apparatus includes the first through fourth mirrors 511 to514, respectively, of the projection system described above withreference to FIG. 5, and an opening limiting aperture 515. As will beunderstood from FIG. 9, the reticle-stage reference mark 3 through whichthe alignment light (non-exposing light) passes is provided, as a resultof which the alignment light arrives at a wafer alignment mark 9 bytraversing only the projection optical system.

[0052] The images of the reticle-stage reference mark 3 and waferalignment mark 9 illuminated by the illuminating optical system 2 aredetected by an alignment detecting optical system 1 comprising an imageforming lens and an image sensing device, and relative positioning ofthe reticle-stage reference mark 4 and wafer alignment mark 9 is carriedout by an image processing detection method. Image processing detectionmethods that can be mentioned are template matching, symmetrical patternmatching and centroid-position detection.

[0053] The relative positional relationship between the reticle-stagereference mark 3 and a reticle alignment mark 6 is detected beforehand,by a method described in FIG. 2, using an optical system indicated atreference numerals 16 to 20 and 30, and the relationship is stored by astorage device 27 for storing the position of the reticle stage.Accordingly, if relative positioning of the reticle-stage reference mark4 and wafer alignment mark 9 is performed, then positioning of thereticle 5 and wafer 10 can be carried out. It should be noted that thewafer 10 is held by a wafer chuck 11 and mounted on a wafer stage 12.

[0054]FIG. 2 is a diagram illustrating a method of detecting therelative positions of the reticle-stage reference mark placed on thereticle stage 4 and the reticle alignment mark 6 placed on the reticle5. Image processing and detection are executed by a detecting opticalsystem 30 comprising an image sensing unit 16 and an image formingoptical system 17, and the relative positional relationship between thereticle-stage reference mark 3 and the reticle alignment mark 6 isdetected. The mechanism (the components indicated by the referencenumerals 16 to 20 and 30), which detects the relative position of thereticle-stage reference mark and reticle alignment mark, shall bereferred to as a first detection mechanism.

[0055] More specifically, first the reticle stage 4 is moved to thedetection position of the detecting optical system 30. The position ofthe reticle-stage reference mark 3 is detected by the detecting opticalsystem 30 and the position of the reticle stage at this time is storedby the storage unit 27. It should be noted that the reticle-stagereference mark of this embodiment is obtained by placing a reticle-stagereference mark comprising an object through which alignment light doesnot pass on an object (membrane) through which the alignment light doespass. The reticle-stage alignment mark can be detected by the detectingoptical system 30. Next, the reticle stage 4 is moved, the position ofthe reticle alignment mark 6 on the reticle 5 is subjected to imageprocessing and detection by the detecting optical system 30, and theposition of the reticle stage 4 at this time is stored by the storageunit 27. The coordinates of the reticle stage 4 when each mark isdetected by the detecting optical system 30 are thus stored in thestorage unit 27. The relative position of the reticle-stage referencemark 3 and reticle alignment mark 6 is detected from these coordinates.

[0056] It should be noted that the detecting optical system 30, a lightsource 18, an illuminating optical system 19 and half-mirror 20 may havemoving mechanisms. When detection of alignment is not carried out, thereis a possibility that the optical system constituted by the detectingoptical system 30, light source 18, illuminating optical system 19 andhalf-mirror 20 will interfere with the operation of other units, as byblocking the exposing light within the exposure apparatus. Hence it ismade possible to retract this optical system to a position at which itwill not interference with other units.

[0057]FIG. 10 is a flowchart useful in describing the procedure ofalignment processing executed according to the first embodiment setforth above. It should be noted that the procedure for alignmenttreatment shown in FIG. 10 is implemented by a control system (notshown) provided on the above-described exposure apparatus.

[0058] When the reticle 5 is mounted on the reticle stage 4 (S101), thereticle stage 4 is moved to a position at which relative position isdetected by a first detection mechanism (S102). The first detectionmechanism detects the relative position of the reticle-stage referencemark 3 and reticle alignment mark 6 (S103) through the proceduredescribed above in connection with FIG. 2.

[0059] When measurement by the first detection mechanism ends, thereticle stage 4 is moved to an alignment measurement position in orderto measure alignment (S104). At this position the alignment light fromthe illuminating optical system 2 shown in FIG. 1 passes through thereticle-stage reference mark 3 and impinges upon the multilayer-mirroroptical system 7. Meanwhile, the wafer stage 12 on which the wafer 10has been mounted also is moved to the alignment measurement position(S105). Under these conditions, the alignment light that has passedthrough the reticle reference mark illuminates the wafer alignment mark9. The alignment detecting optical system 1 detects the light reflectedfrom the wafer alignment mark 9 and measures the relative position ofthe reticle-stage reference mark 3 and wafer alignment mark 9 (S106).

[0060] From the thus obtained relative position (S103) of thereticle-stage reference mark 3 and reticle alignment mark 6 and relativeposition (S106) of the reticle-stage reference mark 3 and waferalignment mark 9, the relative position of the reticle alignment mark 6and wafer alignment mark 9 is decided (S107), thereby completingalignment measurement.

[0061] This ends one series of exposure processing steps. If there is anext wafer, then the processing from steps S104 onward is repeated withregard to this new wafer (S108).

[0062] When the relative positional relationship between thereticle-stage reference mark 3 and reticle alignment mark 6 is detected,the height between the two marks may be detected by detecting thedefocusing characteristic of the images obtained. The detected value isused to adjust the positions of the reticle and wafer along the heightdirection at the time of exposure.

[0063] In accordance with the first embodiment, as described above, (1)the reticle-stage reference mark 3 having a portion through whichnon-exposing light is transmitted is provided; (2) the relative positionof the reticle alignment mark 6 and reticle-stage reference mark 3 isdetected by the detection system (16-19, 30) provided separately of theprojection optical system; and (3) it is possible to perform alignmentmeasurement using alignment light that has passed through thereticle-stage reference mark 3.

[0064] [Second Embodiment]

[0065]FIGS. 3 and 4 are schematic views illustrating a semiconductorexposure apparatus that includes a position detecting apparatusaccording to a second embodiment of the invention. In the firstembodiment, alignment is carried out by illuminating the wafer alignmentmark 9 with non-exposing light that has passed through the reticle-stagereference mark 3. In the second embodiment, alignment is carried out byilluminating a chuck mark 8, which is provided on the wafer chuck 11,with non-exposing light that has passed through the reticle-stagereference mark 3.

[0066] As shown in FIG. 3, the illuminating optical system 2 comprises alight source, which emits non-exposing light, and illuminating optics.The illuminating light from the illuminating optical system 2 isreflected by the half-mirror 13 and mirror 14 so as to illuminate thereticle-stage reference mark 3 disposed on the reticle stage 4 throughthe transparent portion or the aperture of the reticle stage 4. Theilluminating light that has passed through the reticle-stage referencemark 3 passes through the multilayer-mirror optical system 7 andilluminates the chuck mark 8 disposed on the wafer chuck 11.

[0067] The images of the reticle-stage reference mark 3 and chuck mark 8illuminated by the illuminating optical system 2 are detected by thealignment detecting optical system 1 comprising an image forming lensand an image sensing device, and relative positioning of thereticle-stage reference mark 4 and chuck mark 8 is carried out by animage processing detection method. The relative positional relationshipbetween the reticle-stage reference mark 3 and reticle alignment mark 6,as well as the relative positional relationship between the chuck mark 8and wafer alignment mark 9, is detected beforehand, by a methoddescribed later, whereby the relative position of the reticle-stagereference mark 3 and wafer alignment mark 9 is detected so that thereticle 5 and wafer 10 can be positioned relative to each other.

[0068] Described next will be a method of detecting the relativepositional relationship between the reticle-stage reference mark 3 andreticle alignment mark 6 and the relative positional relationshipbetween the chuck mark 8 and wafer alignment mark 9.

[0069] Through a method similar to that described above in connectionwith FIG. 2, the relative positional relationship between thereticle-stage reference mark 3 and reticle alignment mark 6 is found byexecuting image processing and detection using the detection mechanismcomprising the detecting optical system 30, light source 18,illuminating optical system 19 and half-mirror 20, and storing thecoordinates of the positions of the marks in the storage unit 27 forstoring the position of the reticle stage.

[0070] The method of detecting the relative positional relationshipbetween the chuck mark 8 and wafer alignment mark 9 will be describednext with reference to FIG. 4.

[0071] This method is disclosed in Japanese Patent Application Laid-OpenNo. 61-263127 filed by the present applicant. According to this method,the relative positional relationship between the chuck mark 8 and waferalignment mark 9 is detected before the wafer chuck 11 is mounted on thewafer stage 12, which is for being exposed by the exposure apparatus. Asshown in FIG. 4, image processing and detection are executed by adetecting optical system 31, which comprises an image sensing device 24and an image forming optical system 25, disposed externally of theexposure apparatus, and the relative positional relationship between thechuck mark 8 and wafer alignment mark 9 is detected. This detectionsystem (the components indicated by the reference numerals 21 to 25 and31) shall be referred to as a second detection mechanism.

[0072] The detection method includes first using the detecting opticalsystem 31 to detect the position of the chuck mark 8 disposed on amoving stage 26 and storing the position of the moving stage 26 at thistime in a storage unit 29 for storing stage position. Next, the movingstage 26 is moved, the position of the wafer alignment mark 9 on thewafer 10 is subjected to image processing and detection by the detectingoptical system 31, and the position of the moving stage 26 at this timeis stored by the storage unit 29. The relative position of the chuckmark 8 and wafer alignment mark 9 is detected from the coordinates, thusstored in the storage unit 29, of the moving stage 26 when each of themarks is detected by the detecting optical system 31.

[0073] Next, with the wafer 10 being held by the wafer chuck 11 carryingthe chuck mark 8 (the condition in which measurement was carried out bythe method shown in FIG. 4), as shown in FIG. 3, the chuck and wafer aretransported and placed on the wafer stage, which is for being exposed bythe exposure apparatus. The relative positional relationship between thereticle-stage reference mark 3 and chuck mark 8 is then detected, asdescribed in connection with FIG. 3, and the wafer stage 12 is drivenbased upon the information concerning the relative positionalrelationship between the chuck mark 8 and wafer alignment mark 9,thereby performing exposure.

[0074] The processing for the above operation will now be described withreference to the flowchart of FIG. 11. The processing described below isimplemented by a control system (not shown) provided on theabove-described exposure apparatus.

[0075] When a new reticle is mounted, the relative position of thereticle-stage reference mark 3 and reticle alignment mark 6 is detected(S209) by executing the steps S101 to S103 in FIG. 10.

[0076] In a case where a new wafer is mounted, on the other hand, firstthe wafer chuck 11 is mounted on the moving stage 26 and the wafer 10 ismounted on the wafer chuck 11 (S201). The wafer 10 is then moved to theposition at which detection is performed by the second detectionmechanism (S202), and the relative position of the chuck mark 8 andwafer alignment mark 9 is detected by the second detection mechanism(S203). The wafer chuck 11 holding the wafer 10 is then moved onto thewafer stage 12 (S204) and alignment measurement is carried out.

[0077] In alignment measurement, the wafer stage 12 and reticle stage 4are moved to the position for alignment measurement (S205), and therelative position of the reticle-stage reference mark 3 and chuck mark 8is detected by the illuminating optical system 2 and alignment detectingoptical system 1 (S206). Next, the relative position of the reticlealignment mark 6 and wafer alignment mark 9, namely the relativeposition of the reticle and wafer, is decided (S207) based upon therelative position of the reticle-stage reference mark 3 and reticlealignment mark 6 detected at step S109, the relative position of thewafer alignment mark 9 and chuck mark 8 detected at step S203, and therelative position of the reticle-stage reference mark 3 and chuck mark 8measured at step S206.

[0078] This ends one series of exposure processing steps. If there is anext wafer, then the processing from steps S201 onward is repeated withregard to this new wafer (S208).

[0079] Thus, according to the first and second embodiments, the relativeposition of the reticle-stage reference mark 3 and chuck mark 8 isdetected by an on-axis TTL alignment optical system. According to thismethod, alignment measurement and exposure are, broadly speaking,carried out in parallel and the structural restrictions on the alignmentdetection system (restrictions imposed by the projection optical systemin many cases) are eliminated. With regard to designing the alignmentdetection system, therefore, it is unnecessary to take space intoconsideration (within certain limits, of course), the detectionmechanism and the like can be arranged with the highest priority beinggiven to detection precision, and it becomes possible to constructvarious alignment detection systems. Further, stabilized detection rateand high precision can be achieved with a high throughput for a varietyof wafer processes. Further, since the detection system for measuringthe relationship between the reticle-stage reference mark and chuck markin the exposure apparatus is an on-axis TTL alignment optical system,there is also no base line. (A base line is generated when off-axisalignment is performed. Hence there is a discrepancy between theposition of the wafer stage when alignment is performed by an off-axisalignment scope and the position of the wafer stage when exposure isperformed. This discrepancy is eliminated.) This makes it possible toeliminate a cause of poor measurement precision.

[0080] Further, when the relative positional relationship between thechuck mark 8 and wafer alignment mark 9 is detected, the height betweenthe two marks can also be detected by detecting the defocusingcharacteristics of the images obtained.

[0081] When positioning the wafer 10 relative to the reticle 5 in thesecond embodiment, whether to use the chuck mark 8 or the waferalignment mark 9 as the alignment mark on the wafer side may be decidedby detecting the image of the wafer alignment mark 9 using send-a-headwafer, etc. According to measurement using send-a-head wafer, when awafer is exposed by the exposure apparatus, measurement of variousparameters (e.g., verification of offset of an alignment detection valueand verification of alignment signal level) for the exposure apparatus,which are necessary when actual exposure is carried out, is performedbefore the actual exposure operation using a wafer employed in actualexposure or a wafer equivalent thereto. If the S/N ratio or contrast ofthe image signal from the wafer alignment mark 9 is a level thatsatisfies the specifications for alignment measurement, the detectionmethod illustrated in the first embodiment is adopted. If the S/N ratioor contrast of this image signal is a level that does not satisfy thespecifications, then measurement should be performed using the detectionmethod described in the second embodiment (FIG. 11).

[0082] The contrast of the image signal (alignment signal) can be foundfrom (b−a)/(a+b) in FIG. 8, for example, and the S/N ratio can be foundfrom (b−a)/a.

[0083] The above processing will be described with reference to theflowchart of FIG. 12.

[0084] First, through the procedure described at steps S101 to S107 inFIG. 10 and S201 to S204 in FIG. 11, i.e., by the method using the firstand second detection mechanisms, the relative position of the waferalignment mark and reticle alignment mark in the send-a-head waferscheme is measured (S301). The S/N ratio and contrast are detected withregard to the image signal representing the wafer alignment markobtained by this measurement (S302).

[0085] In a case where the S/N ratio and contrast exceed respective onesof predetermined values that have been set for them (“YES” at stepS303), the wafer alignment mark can be used directly when alignmentmeasurement is performed. Control therefore proceeds to step S304, wherethe apparatus is set for carrying out alignment measurement described inthe first embodiment. On the other hand, if at least one of the S/Nratio and contrast falls below the predetermined value that has been setfor it (“NO” at step S303), then it is preferred that alignmentmeasurement be carried out using the chuck mark 8. Thus, the apparatusis set (S305) in such a manner that alignment measurement described inthe second embodiment is executed.

[0086] A process for manufacturing a semiconductor device utilizing theexposure apparatus set forth above will now be described. FIG. 6illustrates the overall flow of a process for manufacturingsemiconductor devices. The circuit for the device is designed at step 1(circuit design). A mask on which the designed circuit pattern has beenformed is fabricated at step 2 (mask fabrication). Meanwhile, a wafer ismanufactured using a material such as silicon or glass at step 3 (wafermanufacture). The actual circuit is formed on the wafer by lithography,using the mask and wafer that have been prepared, at step 4 (waferprocess), which is also referred to as “pre-treatment”. A semiconductorchip is obtained, using the wafer fabricated at step 4, at step 5(assembly), which is also referred to as “posttreatment”. This stepincludes steps such as actual assembly (dicing and bonding) andpackaging (chip encapsulation). The semiconductor device fabricated atstep 5 is subjected to inspections such as an operation verificationtest and durability test at step 6 (inspection). The semiconductordevice is completed through these steps and then is shipped (step 7).The pre- and post-treatments are performed at separate special-purposeplants. Maintenance is carried out on a per-plant basis by theabove-described remote maintenance system. Further, information forproduction management and equipment maintenance is communicated by datacommunication between the pre- and post-treatment plants via theInternet or leased-line network.

[0087]FIG. 7 is a flowchart illustrating the detailed flow of the waferprocess mentioned above. The surface of the wafer is oxidized at step 11(oxidation). An insulating film is formed on the wafer surface at step12 (CVD), electrodes are formed on the wafer by vapor deposition at step13 (electrode formation), and ions are implanted in the wafer at step 14(ion implantation). The wafer is coated with a photoresist at step 15(resist treatment), the wafer is exposed to the circuit pattern of themask to print the pattern onto the wafer by the above-described exposureapparatus at step 16 (exposure), and the exposed wafer is developed atstep 17 (development). Portions other than the developed photoresist areetched away at step 18 (etching), and unnecessary resist left afteretching is performed is removed at step 19 (resist removal). Multiplecircuit patterns are formed on the wafer by implementing these stepsrepeatedly. Since the manufacturing equipment used at each step ismaintained by the remote maintenance system described above,malfunctions can be prevented and quick recovery is possible if amalfunction should happen to occur. As a result, the productivity ofsemiconductor device manufacture can be improved over the prior art.

[0088] Thus, in accordance with the embodiments as described above, in aEUV exposure apparatus, for example, transmittance or reflectivity foralignment light can be optimized for relative positioning of areflecting-type reticle and wafer, and it is possible to obtain analignment signal of excellent S/N ratio or contrast by using areticle-stage reference mark, which has been disposed on a reticlestage, as an alignment mark. This makes highly precise alignmentfeasible. Especially good effects are obtained when position detectionis performed by a TTL scheme. Furthermore, by adopting a reticle-stagereference mark that transmits light, an alignment detecting opticalsystem can be situated above the reticle stage, as shown in FIG. 1. As aresult, the exposing light is no longer blocked, there is greater degreeof freedom in terms of laying out the alignment detecting opticalsystem, and measurement can be carried out without interfering with theexposing light.

[0089] Thus, in accordance with the invention as described above, it ispossible to prevent a decline in the amount of light of an alignmentsignal and to construct a highly precise alignment detecting opticalsystem.

[0090] As many apparently widely different embodiments of the presentinvention can be made without departing from the spirit and scopethereof, it is to be understood that the invention is not limited to thespecific embodiments thereof except as defined in the appended claims.

What is claimed is:
 1. A method of detecting relative position of areflecting-type reticle and substrate, said reticle having an alignmentmark thereon, said method comprising: a holding step of holding thereticle on a reticle stage which has a reference mark; and a firstdetection step of detecting relative position of the reference mark ofthe reticle stage, and the alignment mark on the reticle.
 2. The methodaccording to claim 1, wherein the reference mark on the reticle stage isof the light-transmitting type; said method further comprising a seconddetection step of detecting relative position of the reference mark andan alignment mark on the substrate, by illuminating the alignment markon the substrate with alignment light that has passed through thereference mark.
 3. The method according to claim 2, wherein said seconddetection step includes: a step of illuminating the reference mark withalignment light; a step of illuminating the alignment mark on thesubstrate, with alignment light that has passed through the referencemark; and a step of detecting relative position of the reference markand the alignment mark on the substrate based upon returned lightobtained by illumination of the reference mark and the alignment mark onthe substrate.
 4. The method according to claim 2, further comprising adecision step of deciding relative position of the reticle and substratebased upon the relative position of the reference mark and the alignmentmark on the reticle and the relative position of the reference mark andthe alignment mark on the substrate.
 5. The method according to claim 1,wherein the reference mark disposed on the reticle stage is of thelight-transmitting type; said method further comprising a thirddetection step of detecting relative position of the reference mark anda chuck mark on a substrate chuck holding the substrate, by illuminatingthe chuck mark with alignment light that has passed through thereference mark.
 6. The method according to claim 5, wherein said thirddetection step includes: a step of illuminating the reference mark withalignment light; a step of illuminating the chuck mark with alignmentlight that has passed through the reference mark; and a step ofdetecting relative position of the reference mark and the chuck markbased upon returned light obtained by illumination of the reference markand the chuck mark.
 7. The method according to claim 5, furthercomprising a fourth detection step of detecting relative position of thechuck mark on the substrate chuck and the alignment mark on thesubstrate being held on the substrate chuck.
 8. The method according toclaim 7, further comprising a decision step of deciding relativeposition of the reticle and substrate based upon the relative positionof the reference mark and the alignment mark on the reticle detected bythe first detection step, the relative position of the chuck mark andthe alignment mark on the substrate detected by the fourth detectionstep, and the relative position of the reference mark and the chuck markdetected by the third detection step.
 9. The method according to claim8, wherein it is possible to execute a second detection step ofdetecting relative position of the reference mark and the alignment markon the substrate by illuminating the alignment mark on the substratewith alignment light that has passed through the reference mark; andwhether alignment measurement by said first and second detection stepsor alignment measurement by said first, third and fourth detection stepsis performed is decided based upon status of an image signal thatprevails when the alignment mark on the substrate is detected.
 10. Anapparatus for detecting relative position of a reflecting-type reticleand substrate, the reticle having an alignment mark thereon, saidapparatus comprising: a reticle stage for holding the reticle, saidreticle stage having a reference mark; a first detection system fordetecting relative position of the reference mark and the alignment markon the reticle.
 11. The apparatus according to claim 10, wherein thereference mark on said reticle stage is of the light-transmitting type;said apparatus further comprising a second detection system fordetecting relative position of the reference mark and an alignment markon the substrate, by illuminating the alignment mark on the substratewith alignment light that has passed through the reference mark.
 12. Theapparatus according to claim 11, wherein said second detection systemincludes: a unit for illuminating the reference mark with alignmentlight; a unit for illuminating the alignment mark on the substrate, withalignment light that has passed through the reference mark; and a unitfor detecting relative position of the reference mark and the alignmentmark on the substrate based upon returned light obtained by illuminationof the reference mark and the alignment mark on the substrate.
 13. Theapparatus according to claim 11, further comprising a decision unit fordeciding relative position of the reticle and substrate based upon therelative position of the reference mark and the alignment mark on thereticle and the relative position of the reference mark and thealignment mark on the substrate.
 14. The apparatus according to claim10, wherein the reference mark disposed on said reticle stage is of thelight-transmitting type; said apparatus further comprising a thirddetection system for detecting relative position of the reference markand a chuck mark on a substrate chuck holding the substrate, byilluminating the chuck mark with alignment light that has passed throughthe reference mark.
 15. The apparatus according to claim 14, whereinsaid third detection system includes: a unit for illuminating thereference mark with alignment light; a unit for illuminating the chuckmark with alignment light that has passed through the reference mark;and a unit for detecting relative position of the reference mark and thechuck mark based upon returned light obtained by illumination of thereference mark and the chuck mark.
 16. The apparatus according to claim14, further comprising a fourth detection system for detecting relativeposition of the chuck mark and the alignment mark on the substrate beingheld on the substrate stage.
 17. The apparatus according to claim 16,further comprising a decision unit for deciding relative position of thereticle and substrate based upon the relative position of the referencemark and the alignment mark on the reticle detected by said firstdetection system, the relative position of the chuck mark and thealignment mark on the substrate detected by said fourth detectionsystem, and the relative position of the reference mark and the chuckmark detected by said third detection system.
 18. The apparatusaccording to claim 17, further comprising: a second detection system fordetecting relative position of the reference mark and the alignment markon substrate, by illuminating the substrate alignment mark withalignment light that has passed through the reference mark; and adecision unit for deciding whether to perform alignment measurement bysaid first and second detection systems or by said first, third andfourth detection systems based upon status of an image signal thatprevails when the alignment mark on the substrate is detected.
 19. Theapparatus according to claim 10, wherein the reference mark exhibits atransmitting property with respect to wavelength of the alignment light.20. An exposure apparatus on which is mounted the position detectingapparatus set forth in claim
 10. 21. A device manufacturing methodcomprising steps of transferring a pattern on a reticle to a substrateby exposure using a reticle and a substrate the relative position ofwhich has been detected using the position detection method set forth inclaim 1, and manufacturing a device from the substrate to which thepattern has been transferred by exposure.